It is well known in the prior art that automotive frames and sheet metal can be straightened and returned to substantially their original specifications by engaging the frame or sheet metal with a clamp and pulling the engaged member to restore the damaged part. One such example is shown in U.S. Pat. No. 3,744,838 which, in FIGS. 1 through 5 shows a first design for engaging sheet metal parts, and in FIGS. 6 and 7 a second design for engaging a frame members. A unibody pulling device such as that shown in U.S. Pat. No. 3,355,771, is designed to pull one side of the rail. Since a unibody rail is typically made up of two or more pieces of sheet metal which are formed into a box cross section, these types of clamps do not always pull properly. Thus, on a hard hit pull, this style of clamp can cause the rail to distort and loose its proper box shape. The only proper way to pull a unibody rail, which is typically made of high strength steels, is by pulling on both sides of the damaged rail. Also, if you pull a unibody car rail at one point only with a force of over 2,500 pounds, it is possible to break the sheet metal off at the clamp contact point. This will obviously result in more repair time. However, if the rail is secured at two points the frame technician has an option of using more power, up to perhaps 3,500 pounds, if needed.
When pulling on rails, such as skit rails or upper frame rails, which may not be box shaped, in the past it has been standard proctice to engage these members at one point only. By engaging such members at two longitudinally spaced apart points, additional pulling force can be exerted on the member, and furthermore, a double angle pull can be utilized.